1. Technical Field
Embodiments of the invention relate generally to alignment evaluation and more particularly, but not exclusively, to methods for measuring misalignment of circuit assemblies.
2. Background Art
Alignment accuracy is a critical requirement, in integrated circuit (IC) assemblies, for obtaining reliable electrical interconnections between components for good device operation. Misalignment could lead to an assembled semiconductor device becoming non-functional due to an open circuit or a short defect. Connection integrity problems due to misalignment between a device being attached to a substrate can arise during controlled collapse chip connection (C4) reflow, thermocompression bonding (TCB) or other such processing.
Existing technologies for determining misalignment of integrated circuitry use an x-ray-based approach. These technologies variously generate an image by transmitting x-rays through integrated circuitry after the formation of a connection (or “joint”) that couples the integrated circuitry to a board or other substrate. Based on the imaging, analysis is performed to try measure the quality of the connection, using metrics such as joint geometry and alignment between a circuit and a structure connected thereto.
One drawback of the current techniques is an inability to distinguish between structures having materials with similar x-ray absorption, resulting in incorrect evaluation of joint geometry. The evaluation of connections based on x-ray imaging is prone, for example, to false positives as well as to false negatives. Also, the evaluation of circuitry connectivity based on x-ray imaging does not scale well with the smaller geometries of next-generation fabrication techniques. As such fabrication technologies continue to decrease the size and pitch of bumps, pads and other structures, the risk of misalignment-induced assembly yield loss is expected to increase. Accordingly, conventional techniques for detecting circuit assembly alignment and connection integrity are expected to be inadequate for the future demands of manufacturers.